Vegetable Disease Update 5-24-13

Cucumber/Pickles: Angular leaf spot

Lettuce: Bacterial leaf blight; Bottom Rot

Tomato: Bacterial spot and speck

Strawberry: Leather rot; Angular leaf spot

Cucumber/Pickles

Angular leaf spot – Symptoms are distinct and easily diagnosed. Small water-soaked lesions develop on leaves and expand until they are delimited by larger secondary veins in leaves resulting in angular lesions. After time these lesions turn brown and infected tissue drops-off resulting in ‘shotholes’. Angular leaf spot can be spread by splashing rain, insects, on the hands of workers and on farm machinery. Working in the field when the foliage is wet favors the spread of the disease. The disease can also be spread by blowing wind and in irrigation water. Management of angular leaf spot begins with clean-seed and planting in fields that has been out of cucurbit production for at least 2 years. Cultivating when foliage and soil are wet and irrigating with pond water should be avoided. There are cucumber varieties with resistance. Add label rate of fixed copper + mancozeb to fungicide maintenance program and repeat applications every 7 days.

Lettuce

Bacterial leaf blight – was reported this week on Romaine lettuce. Symptoms include numerous black, irregular ‘greasy’ lesions on leaves. The bacterium can survive on weeds and infected debris left in the field. Abandoned plantings should be thoroughly worked back into the soil to allow decomposition of infected plants. Copper fungicide applied on a regular basis may help to suppress the spread of the disease.

Bottom Rot/Drop – For Bottom rot, apply Endura 70W (boscalid, FRAC code 7) at 8.0 to 11.0 oz 70W/A, or iprodione (FRAC code 2) at 1.5 to 2.0 lb 50WP/A or OLF should be applied one week after transplanting or thinning and 10 and 20 days later. For Lettuce drop, apply Cannonball (fludioxonil, 12) at 7.0 oz 50WP/A (0 day PHI); Endura (FRAC code 7) at 8.0 to 11.0 oz 70WG/A (14 day PHI); or iprodione (FRAC code 2) at 1.5 to 2.0 lb/A (14 DAY PHI); or Quadris (azoxystrobin, 11) at 0.40 – 0.80 fl. oz/1000 row ft. 2.08SC (0 day PHI) beginning one week after transplanting or thinning and again at 10 and 20 days later. Check labels for days to harvest intervals. For more information on control of Bottom rot and Lettuce drop and other important diseases of lettuce please see the 2013 New Jersey Commercial Vegetable Production Recommendations Guide.

Tomato

Bacterial spot and speck – Tomato transplants with suspected symptoms can be treated with streptomycin (Agri-Mycin 17, Agri-Strep, 25) at 1 lb/100 gallons, or 1.25 teaspoon per gallon every 4 to 5 days prior to transplanting. Additionally, Kocide 3000 (copper hydroxide, FRAC code M1) has a greenhouse label for speck and spot control in the greenhouse. Apply ½ to 1.5 TBSP per 1000 sq ft. every 5 to 10 days. Remember, phytotoxicity is an important issue when apply copper in enclosed structures, see label for cautions, restrictions and liabilities. After transplanting, apply Actigard at 0.33 oz 50WG/A (see label for use), or fixed copper (M1) at 1 lb a.i./A plus a mancozeb (Dithane, Manzate, Penncozeb, M3) at 1.5 lb 75DF or OLF, or ManKocide (M1 + M3) at 2.5 to 5.0 lb 61WP/A on a 7 day schedule.

Strawberry –

Leather rot – can infect fruit at any stage. On green fruit, infected areas turn a dark-brown and develop a rough ‘leathery’ appearance. On fully mature (red) fruit little or no color change may occur on infected fruit however, fruit will have an unpleasant smell and taste. The pathogen (Phytophthora cactorum) overwinters in the soil in low-lying spots and becomes active during wet weather. Conditions that favor leather rot development also favor grey mold (Botrytis) development. However, fungicides for Grey mold control are not effective for leather rot control. Applications of a FRAC code 4 fungicide, such as Ridomil Gold SL (mefenoxam) at 1.0 pt/A 4SL or MetaStar (metalaxyl), or phosphite fungicide (FRAC code 33 fungicide), such as K-Phite, Rampart, or ProPhyt, prior to or at harvesting will help suppress leather rot. For more information on controlling leather rot and other important diseases of strawberry please see the 2013 New Jersey Commercial Vegetable Production Recommendations Guide.

Angular leaf spot – Bacterial leaf spot can cause spots on the leaves causing them to die. Infections can also become systemic killing the whole plant. Importantly, the calyx can become infected causing them it prematurely turn brown and reduce marketability of fruit. Fixed coppers applications will help suppress the spread as long as the weather remains dry. Discontinue copper applications in plant injury begins to occur, usually after 4 to 5 applications. Avoid overhead irrigation which will only make problem worse.